The following experiments are planned for the coming year: a) An investigation of the characteristics and determinants of ventilatory response to CO2 in the hypocapnic zone. Hypoxia and/or hyperthermia are employed to induce hypocapnia, and against that background, graded concentrations of inspired CO2 are added to test responses in the usual way. b) The early stages of ventilatory acclimatization to low oxygen pressures is envisioned as a process that includes both acid-base adjustments and central nervous mechanisms that probably reside in the hypothalamus. The latter is hypothesized as a facilitatory system whose activity depends on many variables, including rates of neurohumoral synthesis and degradation. These are being explored. c) The relationship of tonic and phasic motor activity, that characteristically determine FRC on the one hand, and ventilation, on the other, is being studied under conditions of chronic, hypoxic stress. Further, the relationship of these two respiratory processes to general somatic motor phenomena is also being studied, with additional interest in the sleep/wakefulness cycle.